Marketable Securities, Available-for-sale (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Contractual maturity:
ESTIMATED FAIR VALUE	$ 363,058	$ 388,020
Total debt securities
Contractual maturity:
Maturing in one year or less	132,831	68,347
Maturing after one year through three years	193,212	257,595
Maturing after three years	31,494	24,958
ESTIMATED FAIR VALUE	357,537	350,900
Short-term pooled investments
Contractual maturity:
ESTIMATED FAIR VALUE	$ 5,521	$ 37,120

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details